Certain species of plants exhibit at least in the mature stages a tendency to suckering i.e., the formation of subordinate shoots springing from a bud on the stem, so-called axillary buds. This secondary growth has the effect of subverting the maturation of blossoms, fruit, or leaves for ultimate harvesting and is accordingly desirously avoided in cultivation. This tendency is particularly pronounced in the tobacco plant, especially in the maturation stage following topping or decapitation, i.e., the removal of the terminal growth, main leader or stem apex. In other cases, topping or removal of apical meristematic tissue is itself desirably accomplished chemically.
Large leaf tobaccos as grown in the United States have typically been topped at or shortly after flowering, when dark air cured and fire cured types may have 10 to 16 leaves and burley, flue-cured, Maryland or cigar types may have 16 to 20 leaves. Tops (the blossoms) in tobacco tend to suppress sucker growth down the stalk, so when tops are removed rapid and profuse sucker growth occurs at the juncture of the stem and each leaf thus limiting the development of the upper leaves which are by far the most profitable. Also, suckers provide food for young budworms and hornworms in addition to supplying a preferred site for hornworm egg laying. Accordingly, sucker control is essential for commercial cultivation. It is also important for efficient harvesting, as current mechanical harvesters require near-perfect sucker control for proper operation.
Recently, earlier topping in the button stage has been employed as a means of increasing yields and affording better pest control. The resultant increased tendency to sucker had been controlled in the past by hand removal as often as three times in one season. Most recently, control has been achieved by the use of contact chemical control agents, such as methyl caproate in combination with a later application of a systemic agent such as maleic hydrazide which controls subsequent secondary growths. Successful sucker control permits most of the plant resources to be directed into making larger and heavier leaves, with sufficient spread to have desirable quality.
Various contact chemical agents have been tested for improved sucker control including dimethyldodecylamine acetate ("Penar" manufactured by Pennwalt), 1-octanol/1-decanol mixtures (C.sub.6 -C.sub.12) (available, for example as Off-Shoot-T from Proctor and Gamble Co.) the lower alkyl esters of fatty acids (available as Off-Shoot-O from Proctor and Gamble Co.) and Emgard (from Emery Industries, Inc.) and methyl pelargonate (T-61, available from Emery Industries). See Tobacco Science XIV, pp. 65-68 (1970) and XVI, pp. 134-135 (1972). Although results of testing vary, the dual use of the higher fatty alcohol/maleic hydrazide systems proved superior in testing as reported in Tobacco Science XIV, pp. 86-88 (1970), resulting in the lowest sucker numbers and weight per plant with destruction of the primary and secondary buds in the leaf axils contacted.
A more detailed study of the higher fatty alcohol systems in J. Agri. Food Chem. Vol. 15, #16, pp. 972-5 (1967) showed that the C.sub.9 -C.sub.11 species were highly active, more so than the corresponding higher fatty acid methyl ester, whereas higher or lower fatty alcohols were relatively inactive.
The higher fatty alcohols and derivatives thereof are in somewhat short supply, and are relatively expensive. Also such systems require the proper type and amount of surfactant to control translocation and avoid nonselective tissue kill.
In addition to the fatty alcohols (U.S. Pat. No. 3,824,094) the lower alkyl esters thereof (U.S. Pat. No. 3,340,040; Canada 968,176) or the combination thereof with an N-carbamate (U.S. Pat. Nos. 3,438,765 and 3,326,664), the patent literature also evidences as chemical pinching agents polyoxyethylene glycol ester mixtures (U.S. Pat. No. 3,985,541); combinations of carboxylic acid diesters of aliphatic glycols, surfactants and aliphatic alcohols of 8 to 12 carbon atoms (U.S. Pat. No 3,900,307); glycol esters of fatty acids (U.S. Pat. No. 3,900,351); combinations of diethylene glycol monobutyl ether and hydrocarbyl ether derivatives (U.S. Pat. No. 3,713,804); and alcohol/glycol esters of styrene-maleic anhydride copolymers (U.S. Pat. Nos. 3,697,250 or 3,556,763) in the last of which there is compared the performance of polyalkylene glycol ethers.
In the case of certain of these chemical agents consequential metabolic changes are induced in the product leaf which are considered to lower the quality of the tobacco. In other cases, there is evidence of undesirable residues being imparted to the leaf. In still further instances, topical application may involve chlorosis, necrosis or distortion of leaf structure, nodal scars or stem burn.
Accordingly, the development of new and improved contact compositions for control of meristematic tissue at reasonable expense is desired, especially for effective control with minimum damage to the cultivar. Commonly assigned U.S. Pat. No. 4,047,925 discloses the use of alkane diols of 2 to 6 carbon atoms and in particular, 1,3-butanediol, as selective suckering inhibitors for various kinds of plants, including tobacco. As noted in this patent, however, other structurally related alkane diols have been found to demonstrate little, if any, effectiveness for this and related uses. It is therefore apparent that no predicatable relationship exists between the chemical structure of a composition and its ability to effectuate to a useful extent pinching and other desirable phytological responses except in the case of a relatively narrowly defined class of substances.